Synthesis of multicomponent solid forms is an important method of modifying and fine-tuning the most critical physicochemical properties of drug compounds. The design of new multicomponent pharmaceutical materials requires reliable information about the supramolecular arrangement of molecules and detailed description of the intermolecular interactions in the crystal structure. It implies the use of a combination of different experimental and theoretical investigation methods. Organic salts present new challenges for those who develop theoretical approaches describing the structure, spectral properties, and lattice energy Elatt. These crystals consist of closed-shell organic ions interacting through relatively strong hydrogen bonds, which leads to Elatt > 200 kJ/mol. Some technical problems that a user of periodic (solid-state) density functional theory (DFT) programs encounters when calculating the properties of these crystals still remain unsolved, for example, the influence of cell parameter optimization on the Elatt value, wave numbers, relative intensity of Raman-active vibrations in the low-frequency region, etc. In this work, various properties of a new two-component carbendazim maleate crystal were experimentally investigated, and the applicability of different DFT functionals and empirical Grimme corrections to the description of the obtained structural and spectroscopic properties was tested. Based on this, practical recommendations were developed for further theoretical studies of multicomponent organic pharmaceutical crystals.

Co-crystallization of nonsteroidal anti-inflammatory drug fenamates (N-phenylanthranilic acid (N-PA), niflumic acid (NFA), flufenamic acid (FFA), tolfenamic (TFA) and mefenamic acids (MFA)) with 4,4′-bipyridine (BP) has resulted in the formation of co-crystals with a 2:1 molar ratio. The Crystal Packing Similarity analysis has revealed that the packing arrangement of the [N-PA+BP], [TFA+BP] and [MFA+BP] co-crystals consists of discrete fragments of the crystal structures of initial APIs connected to each other by BP molecules. In case of [FFA+BP], the cocrystal contains a previously unseen packing arrangement of FFA molecules which may be a fragment of a new polymorphic FFA form. Differential scanning calorimetry studies show a goodcorrelation between the co-crystal melting temperature and the melting points of the corresponding pure APIs. The enthalpies of co-crystal formation are small, which indicates that the packing energy gain only originates from weak van der Waals interactions between the API and BP molecules.

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The reaction of GeHal4 with MeN(CH2CH2OSiMe3)2 affords dihalogermocanes MeN(CH2 CH2O)2GeHal2 (1, Hal = Br; 2, Hal = Cl). Treatment of Me2Ge(NMe2)2 with MeN(CH2CH2OH)2 leads to dimethylgermocane MeN(CH2CH2O)2GeMe2 (3). The composition and structure of 1-3 were established by elemental analyses, 1H, 13C NMR spectroscopy, and mass spectrometry. The crystal structure of 1 is reported; structural data obtained from geometry DFT optimization on 1 are in good agreement with experimental results. Values of the electron density in the N→Ge bond critical point and the Laplacian of charge density for 1-3 indicate a closed-shell interaction between the Ge and N atoms.

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